Devices and methods for measuring a three-dimensional shape of a measurement target by any of various methods such as, for example, a light-section method, a focus method, a spatial coding method, a phase shift method, a stereo method, a photogrammetric method, a SLAM method and the like have been proposed and put into practice. For example, a shape measuring device described in Patent Document 1 is operated as follows. Light for projection passes a lattice-pattern plate to be lattice-pattern light. This light is projected onto, and reflected by, a measurement target. An image of the reflected light is captured. Based on the image, a three-dimensional shape of the measurement target is measured. In the field of dental treatment in recent years, such a shape measuring device is used to measure a three-dimensional shape of a dental arch. Thus, such a shape measuring device is applied for, for example, producing artificial teeth and designing prostheses.
However, the measuring device described in Patent Document 1 (measuring device Z in FIG. 11A) is not usable to measure, for example, the entirety of a dental arch Da, which expands over a wide measurement range in an intraoral space, which is narrow, at one time. The reason is as follows. The dental arch as the image capturing subject has a complicated shape, and there are many dead angles in the case where image capturing is performed merely once. The resultant three-dimensional data has many missing parts.
For the above-described reason, the measurement needs to be performed as follows. As shown in FIG. 11A, a plurality of narrow ranges Rn, each of which is a part of the measurement target, are measured (hereinafter, referred to as “narrow range measurement”). The narrow ranges Rn are defined such that the narrow ranges Rn cover the entirety of the wide measurement target and also such that adjacent narrow ranges Rn have overlap portions Rr. FIG. 11B shows narrow range measurement results In′. As shown in FIG. 11C, the adjacent narrow range measurement results In′ are joined together based on the overlap portions Rr. As a result, an entire measurement result Ic′ is acquired as the measurement result on the entirety of the wide measurement target.
However, when two adjacent narrow range measurement results In′ are joined together, there occurs an error although being small. As shown in FIG. 11D, when such adjacent narrow range measurement results In′ are joined together sequentially to form the entire measurement result Ic′, such small errors are accumulated. As a result, the entire measurement result Ic′ may undesirably have a large error.